1. Field of the Invention
This invention relates broadly to surgical instruments. More particularly, this invention relates to a surgical snare instrument for excising polyps.
2. State of the Art
Polypectomy snare instruments are used for the endoscopic removal of hypertrophic tissue growths within a body cavity, and particularly within the colon. Polypectomy snare instruments generally include an elongate tubular member, such as a catheter sheath, a shaft extending through the tubular member, an elastic wire forming a snare (loop) at the distal end of the shaft, and a handle for moving the shaft distally and proximally within the tubular member. The snare can be opened by moving the snare beyond the distal end of the sheath and closed by retraction of the snare into the tubular member, each effected by movement of the shift relative to the sheath.
In operation, a physician introduces the distal end of the instrument, with the snare of the snare instrument in a retracted position, through the working channel of an endoscope until the sheath begins to extend out of the distal end of the endoscope. The physician then directs an assistant, who has control of the handle of the snare instrument, to open the snare. The assistant accomplishes this function by moving two portions of the handle relative to each other. The physician then advances and retracts the sheath into and out of the endoscope, while applying torque to some portion of the instrument to position the snare loop over and around a polyp. Once the snare loop is positioned around the polyp, the physician orders the assistant to close the snare around the polyp. Then, the physician or assistant energizes a source of electrocautery current coupled to the shaft to desiccate, sever, and cauterize the polyp. Finally, the polyp is removed by withdrawing the snare (or, in some cases, the polyp is retrieved by use of another instrument such as a biopsy forceps). In a variation of the procedure, the physician uses suction applied to a channel of the endoscope to remove the polyp or to hold it to the end of the endoscope.
Prior art snare instruments have several problems. First, it is difficult for the physician to precisely position the snare because the physician relies on gripping the small, slippery sheath over the shaft near where the sheath enters the endoscope handle. Typically, it is necessary for the physician to repeatedly push, pull, and torque the sheath and the shaft of the instrument in order to achieve the desired position with the snare around the polyp. Second, the prior art instruments are not capable of efficient steering, because the shaft which is generally used is a cable having low torsional stiffness, and is not usually free of camber or "set". The result of these defects is that when the instrument is used in a tightly-flexed endoscope, the distal end of the snare does not respond directly to torsional input on the shaft where it enters the endoscope handle; i.e., rather than directly respond to torsional input from the physician, the shaft stores the torsional force and upon reaching a threshold, uncontrollable rotationally whips to release the force. Third, while several attempts have been made at providing a snare instrument with a handle adapted to more adeptly steer the snare, most of such prior art instruments do not specifically allow for rotating the snare to position it relative to the polyp. Rather, the physician must rotate the shaft of the instrument by tightly gripping and rotating the sheath where it enters the endoscope to try to maneuver the snare over the polyp. In addition, in the several prior art devices specifically adapted for rotational control, e.g., U.S. Pat. No. 5,066,295 to Kozak et al. and U.S. Pat. Nos. 3,955,587, 4,256,113, and 4,294,254 to Chamness et al., the rotational control function is placed in the handle at the proximal end of the instrument. This handle then controls the extension and retraction of the snare loop as well as the rotation of the snare loop. However, this handle is typically held by the assistant, so the physician must orally direct the assistant to coordinate the handle controls while the physician moves the jacket in and out of the endoscope. As a result, these instruments have not been widely accepted by physicians.